As known in the art, a switching voltage regulator (SVR) receives an electrical power from a source such as, for example, a battery or AC-DC rectifier, and outputs electrical power at a controlled or regulated voltage.
A typical SVR includes transistor-based switching circuits, which may be referenced as “actives,” connected to reactive elements, i.e., inductors and capacitors, which may be referenced as “passives.” The transistor-based switching circuits may be implemented, at least in part, with integrated circuitry. However, typically, one or more of the reactive elements has a large value (i.e., microfarads or microhenrys) and, therefore, cannot be practically implemented in the integrated circuit with the actives. This is particularly true for high power applications where high switching currents through the reactive elements require low electrical resistance and low stray reactance.
For SVRs in portable electronic equipment such as, for example, laptop computers, “smart phones” other kinds of personal digital assistants (PDAs), smaller size and good dissipation of heat are becoming increasingly important as design requirements.
Heat dissipation is an increasing problem with SVRs, because their power requirements are increasing. The power requirement is increasing because of increasing demand for computational power in portable electronic equipment. Increasing computational power requires more complex semiconductor circuits, i.e., more transistors and interconnects, and higher clock speed that, in turn, increases power consumption.
The SVR heat dissipation problem is often exacerbated because, in addition to delivering more power, the SVR must be physically smaller packages.
In addition, there is increasing demand for improved power efficiency in SVRs. For example, resistive loss wastes battery power, lowers the power actually delivered by the SVR, and increases the heat the SVR generates. Since the structure of the SVR must accommodate this heat, but the heat represents wasted power, the SVR design or the powered circuit design may have to be compromised, to meet overall power and heat budget.
The concurrent demand for SVR higher power and smaller SVR packages, presents problems that are difficult to solve with present SVR circuit technologies.
For example, SVRs require large value output inductors. Because of high current and low resistance requirements, these SVR inductors are generally implemented as separate components, packaged and arranged in a manner occupying area on a substrate and often requiring long connection paths.
The present inventors have identified that Low Temperature Co-Fired Ceramic (LTCC) inductors have characteristics that, if LTCCs were suitable for SVRs, would provide benefits. However, known LTCC inductors are generally unsuitable for high current applications such as, for example, power supplies or voltage regulators. They are unsuitable because the inductive elements are thin, high resistance conductors that cannot carry high current.
Stated more specifically, the conductors in known LTCC inductors are made by screen-printing conductive ink patterns (e.g. comprising silver particles) on sheets of green (i.e. unfired) ferromagnetic ceramic material. Multiple green sheets with printed conductor patterns are then stacked and fired at high temperature, causing the sheets and conductive ink to bond by sintering. The printed conductors are thin; typically conductive ink is about 0.001″ thick, and the green sheets are about 0.002-0.005″ thick. The conductive ink is applied as a printed film because the green ceramic sheets must be close enough to one another to fuse by sintering. Because of the printed conductor structure of LTCC inductors, the conductive wiring formed from the conductive ink is too thin to carry large currents.
Related to having thin conductors, another shortcoming of known LTCC inductors is that the ferromagnetic ceramic material is typically a poor heat conductor.
These and other limitations and shortcomings have prevented LTCC inductors from being used in high power electronics applications and, instead, has relegated LTCC inductors to applications such as RF filters, tuners and the like.
Prior art high power SVRs are therefore constructed with discrete inductors and associated connections, with resulting resistive losses and stray reactance. Further, the discrete inductors and other structural features of prior art SVRs often result in heat sources, requiring heat conduction and heat sink structures that occupy volume. Further, the discrete inductors and other structural features of prior art SVRs often require that the heat sources be arranged for practical thermal connection with heat sinks, and these arrangements may compromise the electrical performance of the SVR.